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Solution failure in a Step>1, it could be due to: The solution may be at a buckling or limit point, i.e., displacements grow large under constant forces. If so, for force control or contact problems, this is the end of solution (check out the response

Question asked by David Rodríguez on Mar 24, 2018
Latest reply on Mar 25, 2018 by Ryan Dark

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I am getting this when I tried to simulate this non-linear study

Solution failure in a Step>1, it could be due to: The solution may be at a buckling or limit point, i.e., displacements grow large under constant forces. If so,

for force control or contact problems, this is the end of solution (check out the response graphs).

The solver numerical difficulties:

1. Reduce the Singularity-elimination-factor (.5 or 0.)

2. For Plasticity models, raise ETAN >Ex/100.

3. For Nitinol, or large strain plasticity, set:

Maximum-Strain-Inc.=(or >)1. (0.01 defaults to 1.)

Ryan Dark Mar 24, 2018 7:35 PM

Correct Answer

Hi David,

There is only an assembly file attached but none of the parts. Could you post up a new .ZIP that has the assembly and the part files for us to take a look through/

See the reply in context

Attachments

Test Setup - Hex Nut.SLDASM.zip3.1 MB

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Ryan Dark Mar 24, 2018 7:35 PM

Hi David,

There is only an assembly file attached but none of the parts. Could you post up a new .ZIP that has the assembly and the part files for us to take a look through/

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David Rodríguez @ Ryan Dark on Mar 24, 2018 9:28 PM

Hi Ryan,

thank you for responding I am attaching a complete folder where all my parts are.

Thanks for your help

Attachments

Test Setup.zip18.3 MB

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Ryan Dark @ David Rodríguez on Mar 24, 2018 10:52 PM

Since you already marked that correct I guess I have to deliver now. No pressure.

There are a couple pretty big issues inside your setup.

You have an axis symmetric model but you have chosen the Plane Stress 2D simplification type. This would assume your cross section is thin but uniform in one direction. This is definitely not an accurate description of your 3D model so change this over to the "Axi-Symmetric"-type of 2D simplification using one of the temporary axis down the bolt.
I am assuming that you are interested in the stress inside of the nut/thread interface. Because of this you would not wish to place the fixture on the nut because it will if a deleterious effect on your stress results in that general region of the model. It will cause the nut to be stiffer than it would otherwise be and lead to stress singularities in the area around the fixture. it would be best to reverse your positions of the applied force and the fixture so the fixture is as far from the region of interest on the model as you can make it.

That accounts for the big on the setup. There were a couple things that had to be done to make the study run though.

Having the Global Contact set to No Penetration was not picking up the interaction between the nut threads and the shaft threads so I had to create Contact Sets for No Penetration on the 5 interacting threads.
The default initial pseudo-time step being set to 0.01 was causing the analysis to not find equilibrium in the first step until the time step was automatically reduced to a much lower value. I changed the initial time step to 0.00001 (an arbitrary small number) so it wouldn't have try to find the smaller initial time step. The other pseudo-time settings were left alone so as the solver progressed it would go back to normal larger time steps.

With all that in place there are results to look at.

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David Rodríguez @ Ryan Dark on Mar 25, 2018 12:54 AM

Hi, Ryan

Thank you again for the help.

I have modified all the parameters you mentioned but I am still getting errors. Could you please attach the files that you created so I can compare all the settings you changed.

This is the errors I am getting right now

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Ryan Dark @ David Rodríguez on Mar 25, 2018 1:20 AM

David,

Why don't you post up what you have now and we'll find the difference.

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David Rodríguez @ Ryan Dark on Mar 25, 2018 10:42 AM

Ryan,

I am attaching the new study with all the parts. It looks like the previous study is in the folder too but please check the one with the Axi-Symmetric part

Attachments

Test Setup.zip10.7 MB

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Ryan Dark @ David Rodríguez on Mar 25, 2018 1:17 PM

It looks like you have left the Global Contact No Penetration in place and it is leading to an issue with recognizing the No Penetration Contact Sets. I'm not too sure why that is but I had deleted that Global Contact in my own setup so the study could only use the contacts I made manually. That difference and that the mesh is set to Blended Curvature whereas my own is set to just Curvature. The mesh type does also seem to play into whether the contacts are recognized or not as the intermediate results show the nut detaching from the shaft after a couple steps then becoming unstable thereafter.

So, delete the Global Contact, change to Curvature mesh and it looks like you have a functioning study.

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7 Replies

Ryan Dark Mar 24, 2018 7:35 PM
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Correct Answer
Hi David,
There is only an assembly file attached but none of the parts. Could you post up a new .ZIP that has the assembly and the part files for us to take a look through/
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- David Rodríguez @ Ryan Dark on Mar 24, 2018 9:28 PM
  Mark Correct
  Correct Answer
  Hi Ryan,
  
  thank you for responding I am attaching a complete folder where all my parts are.
  
  Thanks for your help
  Attachments
  - Test Setup.zip18.3 MB
  Like • Show 0 Likes0
  Actions
  - Ryan Dark @ David Rodríguez on Mar 24, 2018 10:52 PM
    Mark Correct
    Correct Answer
    Since you already marked that correct I guess I have to deliver now. No pressure.
    
    There are a couple pretty big issues inside your setup.
    You have an axis symmetric model but you have chosen the Plane Stress 2D simplification type. This would assume your cross section is thin but uniform in one direction. This is definitely not an accurate description of your 3D model so change this over to the "Axi-Symmetric"-type of 2D simplification using one of the temporary axis down the bolt.
    I am assuming that you are interested in the stress inside of the nut/thread interface. Because of this you would not wish to place the fixture on the nut because it will if a deleterious effect on your stress results in that general region of the model. It will cause the nut to be stiffer than it would otherwise be and lead to stress singularities in the area around the fixture. it would be best to reverse your positions of the applied force and the fixture so the fixture is as far from the region of interest on the model as you can make it.
    That accounts for the big on the setup. There were a couple things that had to be done to make the study run though.
    Having the Global Contact set to No Penetration was not picking up the interaction between the nut threads and the shaft threads so I had to create Contact Sets for No Penetration on the 5 interacting threads.
    The default initial pseudo-time step being set to 0.01 was causing the analysis to not find equilibrium in the first step until the time step was automatically reduced to a much lower value. I changed the initial time step to 0.00001 (an arbitrary small number) so it wouldn't have try to find the smaller initial time step. The other pseudo-time settings were left alone so as the solver progressed it would go back to normal larger time steps.
    With all that in place there are results to look at.
    Like • Show 0 Likes0
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    - David Rodríguez @ Ryan Dark on Mar 25, 2018 12:54 AM
      Mark Correct
      Correct Answer
      Hi, Ryan
      
      Thank you again for the help.
      
      I have modified all the parameters you mentioned but I am still getting errors. Could you please attach the files that you created so I can compare all the settings you changed.
      
      This is the errors I am getting right now
      
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      - Ryan Dark @ David Rodríguez on Mar 25, 2018 1:20 AM
        Mark Correct
        Correct Answer
        David,
        Why don't you post up what you have now and we'll find the difference.
        Like • Show 0 Likes0
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        David Rodríguez @ Ryan Dark on Mar 25, 2018 10:42 AM
        Mark Correct
        Correct Answer
        Ryan,
        
        I am attaching the new study with all the parts. It looks like the previous study is in the folder too but please check the one with the Axi-Symmetric part
        
        Attachments
        Test Setup.zip10.7 MB
        Like • Show 0 Likes0
        Actions
        Ryan Dark @ David Rodríguez on Mar 25, 2018 1:17 PM
        Mark Correct
        Correct Answer
        It looks like you have left the Global Contact No Penetration in place and it is leading to an issue with recognizing the No Penetration Contact Sets. I'm not too sure why that is but I had deleted that Global Contact in my own setup so the study could only use the contacts I made manually. That difference and that the mesh is set to Blended Curvature whereas my own is set to just Curvature. The mesh type does also seem to play into whether the contacts are recognized or not as the intermediate results show the nut detaching from the shaft after a couple steps then becoming unstable thereafter.
        
        So, delete the Global Contact, change to Curvature mesh and it looks like you have a functioning study.
        Like • Show 0 Likes0
        Actions

Solution failure in a Step>1, it could be due to: The solution may be at a buckling or limit point, i.e., displacements grow large under constant forces. If so, for force control or contact problems, this is the end of solution (check out the response

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